Heat exchangers of the type to which the present invention is directed are well known in the art. They are used, for example, as recuperators for turbine engines and the like.
Such heat exchangers are madde up of a plurality of annular plates. Each annular plate has sets of first and second gas ports formed therein, the first and second gas ports of the sets being arranged alternately thereabout. The plates are arranged in pairs and the plates of a pair are superposed one upon the other with their respective first and second sets of gas ports aligned. The plates of a pair are joined together by continuous weld lines extending about each of their aligned first and second gas ports.
The plates of a pair are essentially identical with the exception that the areas of the plates between their arrays of alternate first and second gas ports are given different configurations. When the plates are welded together, their surface configuration cooperate to slightly space the plates from each other in those areas between its first and second gas ports so that gases can pass between the plates of the pair. In a given heat exchanger, as many as two hundred or more pairs of plates are stacked with their first and second sets of gas ports aligned. The plate pairs are joined together by being welded at their outer edges. In use, through appropriate ducting and manifolding gases pass through the aligned sets of first gas ports in the stack of plate pairs, and return through the aligned sets of second gas ports. In the meantime, hot spent gases pass between the plates of each pair in heat exchange relationship with those gases passing through the aligned gas ports.
It is important that the welds about each of the first and second gas ports of each heat exchanger plate pair be continuous and leak-free so that the gases passing through the first and second gas ports are completely isolated from the hot spent gases passing between the plates of each pair. Heretofore, the welds in question were inspected visually. This method of inspection is not only time consuming, but also is far from fool-proof.
The present invention is based upon the development of a fixture which will receive a welded pair of heat exchanger plates and will form a discrete sealed chamber about each of the weld lines of the plate pair and the gas port about which that weld line extends. Each of the sealed chambers is connected to its own leak detector. Means are provided to introduce air under pressure between the plates of the pair being tested. Should any one of the continuous weld lines be faulty, air will leak into its respective chamber and will be detected by its respective sensor. Means are provided to record any leak which might occur and means may also be provided to mark the faulty weld line.
The test apparatus or fixture of the present invention is simple in construction. The apparatus is capable of detecting and identifying extremely small leaks and the entire test sequence for a welded pair of heat exchanger plates can be accomplished very rapidly.
The method of the present invention includes the steps of locating the plate pair to be tested within the fixture, closing the fixture upon the plate pair, clamping the fixture in closed position, sealing the individual chambers about the weld lines, introducing pressurized air between the plates of the pair being tested, logging the data generated by the test, unclamping the fixture, opening the fixture, marking any faulty weld line discovered by the test, and removing the tested pair of plates from the fixture.
The apparatus and method of the present invention lend themselves well to total automation. The operation of the apparatus or fixture can be computer controlled, and the loading or unloading of plate pairs into and out of the apparatus can be accomplished by robot means.